Vacuum valves for the substantially gastight closing of a flow path which leads through an opening shaped in a valve housing are commonly known in different embodiments from the prior art. Vacuum gate valves are used, in particular, in the field of IC and semiconductor production, which must take place in a protected atmosphere, as far as possible without the presence of contaminating particles. For instance, in a production plant for semiconductor wafers or liquid crystal substrates, the highly sensitive semiconductor or liquid crystal elements pass sequentially through a plurality of process chambers, in which the semiconductor elements located within the process chamber are machined by means of, in each case, a machining device. Both during the machining process within the process chamber and during the transport from process chamber to process chamber, the highly sensitive semiconductor elements must be constantly in a protected atmosphere—in particular in a vacuum. The process chambers are connected to each other, for instance, via connecting passages, wherein the process chambers can be opened by means of vacuum gate valves for transfer of the parts from one to the next process chamber and, subsequent to implementation of the respective production step, closed in a gastight manner. Due to the described field of application, valves of this type are also referred to as vacuum transfer valves and, due to their rectangular opening cross section, also as rectangular gate valves.
Since transfer valves are used, inter alia, in the manufacture of highly sensitive semiconductor elements, the particle generation caused, in particular, by the actuation of the valve, and the number of free particles in the valve chamber, must be kept as low as possible. The particle generation is primarily a consequence of friction, for instance by metal-metal contact and by abrasion.
The sealing can be effected, for example, either via a seal disposed on the closure side of the closure plate, which seal is pressed onto the valve seat surrounding the opening, or via a sealing ring on the valve seat, against which the closure side of the closure plate is pressed. Different sealing devices are known from the prior art, for instance from U.S. Pat. No. 6,629,682 B2 (Duelli). A suitable material for sealing rings is, for instance, the elastic sealing material known under the trade name Viton®.
The requirements which are placed on the seals used in vacuum valves are very high. On the one hand, in the closed state of the valve, the leak-tightness of the valve must be ensured. This is a big challenge, above all due to the, in the vacuum sector, high differential pressures, and the thus generated large forces acting on the valve shutter. Since, in the case of excessively high compressions, the seals used are subjected to above-average, high wear or are destroyed, the structure of the valve must be such that the differential pressure forces cannot, or can only to a limited degree, act on the seals. The compression of the seal should be effected as evenly as possible along its course, which calls for a uniform pressing force of the valve disk upon the valve seat throughout the contact zone. Above all, transverse loads and longitudinal loads upon the seal should be kept as low as possible. In the case of transverse loads transversely to the longitudinal direction of the seal, in O-ring seals there is the danger that they will be torn out of their mounting, in particular the groove, in which they are fixed. Vulcanized-on seals, too, may only be exposed to very limited transverse forces. Both in the open and in the closed state of the valve, the seals are in part exposed to aggressive mediums and must therefore either be of such a nature that they can withstand the influences, and/or are moved out of the flow path of the medium, also in order to avoid abrasion.
Excessively high wear upon the seal represents an uncertainty factor for process reliability and calls for a regular exchange of the seal, which in turn leads to increased downtimes within the process.
Different embodiments of vacuum valves, in particular their sealing and drive technologies, are known from the prior art, which embodiments have, inter alia, the aim of increasing the service life of the seals used and also have improved process reliability.
Depending on the respective drive technologies, a distinction is drawn, in particular, between gate valves, also termed spool valves or rectangular gate valves, and shuttle valves, wherein in the prior art the closing and opening is generally effected in two steps. In a first step, a valve shutter member, in particular a closure plate or a closure element, in the case of a gate valve, as is known, for instance, from U.S. Pat. No. 6,416,037 (Geiser) or U.S. Pat. No. 6,056,266 (Blecha), in particular an L-type gate valve, is linearly displaced over an opening in a motion substantially parallel to the valve seat, or in the case of a shuttle valve, as is known, for instance, from U.S. Pat. No. 6,089,537 (Olmsted), is pivoted over the opening about a pivot axis, without contact being made between the closure plate and the valve seat of the valve housing. In a second step, the closure plate is pressed with its closure side onto the valve seat of the valve housing, so that the opening is closed in a gastight manner. The sealing can be realized, for example, either via a seal disposed on the closure side of the closure plate, which seal is pressed onto the valve seat surrounding the opening, or via a sealing ring on the valve seat, against which the closure side of the closure plate is pressed. The seal, in particular the sealing ring, can be held in a groove and/or vulcanized on.
The described two-stage motion, in which the closure member is firstly slid transversely over the opening without the seal making contact with the valve seat, and the closure member is subsequently pressed substantially perpendicularly onto the valve seat, has, besides the possibility of precise regulation of the flow, above all the advantage that the seal is compressed almost exclusively perpendicularly, without this resulting in a transverse or longitudinal load on the seal. The drive has a relatively complex structure, which in particular is formed either by a single drive, which enables an L-shaped motion of the closure member, or by a plurality of drives, for instance two linear drives or one linear drive and a spreading drive. Spreading drives, which are generally disposed directly behind the closure plate and displace this, relative to the shank on which they are found, in the perpendicular direction onto the valve seat, have inside the valve a multiplicity of mechanical parts which perform relative motions with respect to one another.
Wedge valves, which are adjusted only linearly, enable a significantly higher adjustment speed, yet, due to the transverse loading of the seal, are in part barely suitable for the vacuum sector, and if at all, then only for a small number of adjustment cycles.
This problem is solved by means of gate valves in which, even though the closing and sealing operation is effected via a single linear motion, the sealing geometry is such that a transverse loading of the seal is wholly avoided. Such a valve is, for instance, the transfer valve known under product designation “MONOVAT Series 02 and 03”, and configured as a rectangular insert valve, of the company VAT Vakuumventile AG in Haag, Switzerland. The structure and working method of such a valve are described, for instance, in U.S. Pat. No. 4,809,950 (Geiser) and U.S. Pat. No. 4,881,717 (Geiser).
The valve which is described there possesses in its housing a sealing surface, which, viewed in the direction of the axis of the valve passage opening, possesses portions situated one behind the other, which, via smooth curves, pass into laterally outward running, flat sealing surface portions, wherein the imaginary generatrices of this sealing surface, which is in one piece yet has a plurality of portions, lie parallel to the axis of the valve passage opening. The sealing surface is machine-worked. The closure member possesses a thereto corresponding bearing surface for the peripherally closed seal. Described in greater detail, the so-called valve slide possesses a valve housing and a valve passage opening, which can be closed with a closure member which is displaceable in its plane. In the region of the valve passage opening is provided a sealing surface, against which, in the closing position of the closure member, bears a peripherally closed seal disposed on said closure member, wherein the imaginary, straight generatrices of the sealing surface lie parallel to the axis of the valve passage opening. The peripherally closed, one-piece seal has portions of different lengths and/or shapes, which lie in different planes, wherein two main portions of the peripherally closed seal lie in planes which stand at right angles to the axis of the valve passage opening and are spaced apart. The two main portions of the seal are connected by side portions. The closure member possesses, in relative to the course of the sealing surface of the housing, a correspondingly running face supporting the peripherally closed seal. The side portions of the peripherally closed seal extend in a U-shape. Respectively the branches of these side portions extending in a U-shape lie in one plane. Those portions of the sealing surface which, viewed in the axial direction of the valve passage opening, lie one behind the other, for the contact of the main portions of the seal in that region in which they possess a common, straight, axis-parallel generatrix, pass into laterally outward running flat sealing surface portions. These flat sealing surface portions lie in planes lying parallel to one another and to the axis of the valve passage opening.
A suitable drive for such a transfer valve which can be closed by means of a linear motion is represented in JP 6241344 (Buriida Fuuberuto). The drive which is described there possesses eccentrically mounted levers for the linear displacement of the push rods on which the closure member is mounted.
Substantially independent of the above-stated drive technologies for valve shutters are the designs for seals provided or applied on the closure element. As mentioned above, such a seal is typically realized as an O-ring in a groove or—for improved durability—is vulcanized onto the closure element by means of a special tool.
For the vulcanization of the seal, overflow gaps are provided in order that an excess of sealing material, for example elastomer, can be led off and the seal 100 can be created in accordance with the shape predefined by the tool (cf. FIG. 1a). However, the material 101,101′ discharged through the overflow gaps remains on the plate blank 110, which is produced, for instance, from aluminum or special steel and has to be mechanically removed subsequent to the vulcanization. This removal is currently generally effected by means of trimming in the region of the metal/sealing material transition zone and results in a removal of both sealing material and metal, as shown in the regions 101 and 101′ of FIG. 1b. 
However, a major drawback with this process is the formation of particles and the formation of burrs in the removal of material by the trimming. Since precisely this particle formation and the lingering of such particles on the valve shutter element is extremely critical for the machining processes to be carried out in the vacuum sector, every effort has to be made to reduce or, ideally, totally avoid such particles.